(a) Description of the Prior Art
In the reproduction of large production engineering drawings, large loft drawings and body drafts, the size of the original drawing to be reproduced, in many cases, may require it to be shipped to a special facility for photographic processing to make the necessary copies. Drawings of this type are generally made on large sheets of dimensionally stable material. The drawings themselves are, in many cases, in a constant process from day to day of being added to or changed in their detail. Copies of the drawings as they change should be made to provide up-to-date information to associated tool and die makers to eliminate delay in their operations. Portable exposure machines and those of the travelling light type are known to the prior art and such are disclosed in U.S. Pat. Nos. 2,292,668; 2,550,640; 3,254,856; 3,385,192. Some prior art photographic exposure units such as that shown and described in Zeunen et al, U.S. Pat. No. Re 28,770, sometimes employ static electricity in order to hold the film and drawing to be reproduced closely together during exposure. This approach requires long tables 20 or 30 feet in length or greater which are in a stationary position with lights and exposure units travelling over them. The efficiency of this type of unit is impaired because a large amount of set-up time is involved. In making the exposure, either a vacuum must be created or an electrostatic unit used. The original engineering drawings may be of a length as great as 50 feet and on an enlarged table, because of the length, would have to be spliced and aligned together for several exposures.
The apparatus according to the present invention is capable of running a continuous run, i.e., a continuous reproduction of an almost unlimited length engineering drawing without doing any splicing. Furthermore, the unit, in accordance with the present invention, requires very little mantime and floor space to make the reproductions. Viewing the efficiency in terms of time to make the reproduction, the present invention permits reproductions of large drawings to be made in about one third of the time possible with prior art systems.
(b) Field of the Invention
This invention relates to improvements in photographic exposure units of the type used to expose large sheets of film for production of extremely accurate photographic reproductions of the original drawing.